1. Technical Field
The present invention relates to multi-optical axis photoelectric sensors having a light projector and a light receiver, the light projector being equipped with a plurality of light projecting elements arranged in a line inside a housing, and the light receiver being equipped with a plurality of light receiving elements for receiving light from the light projecting elements arranged in a line in a longitudinal direction of the housing, the light projector and the light receiver being disposed so that light from each of the light projecting elements is projected to the corresponding each of the light receiving elements to thereby constitute multiple light axis, and in particular, to a multi-optical axis photoelectric sensor having a display portion for displaying an operation state of the multi-optical axis photoelectric sensor on the front surface of the housing.
2. Related Art
As shown in FIG. 10, a typical multi-optical axis electronic sensor is configured by a light projector 100 and a light receiver 200, the light projector 100 being equipped with a plurality of light projecting elements 102 arranged in a line in a longitudinal direction inside a housing 101 having a rectangular shape, and the light receiver 200 being equipped with light receiving elements 202 of the same number as the light projecting elements 102 arranged in a line in a longitudinal direction inside a housing 201 having the same rectangular shape. The light projector 100 and the light receiver 200 are disposed at an adequate distance so that light from each of the light projecting elements 102 is projected to the corresponding each of the light receiving elements 202 to thereby constitute multiple light axis. Optical axes L connecting the respective light projecting elements 102 and the respective light receiving elements 202 are parallel to each other, and form a two-dimensional object detecting area for detecting the presence of an object. The light projector 100 and the light receiver 200 cause each of the light projecting elements 102 of the light projector 100 to sequentially emit light, and each of the light receiving elements 202 of the light receiver 200 corresponding to each of the light projecting elements 102 to perform the light receiving operation, respectively. The light shielding state of each of the optical axes L is detected by turns based on the light receiving quantity of the light at each of the light receiving elements 202, and whether or not an object is in the object detecting area is determined.
At least one (both in the illustrated example) of the light projector 100 and the light receiver 200 incorporates a plurality of light emitting elements 103 for displaying an operation state of the multi-optical axis photoelectric sensor (see. e.g., Japanese Unexamined Patent Publication No. 2008-180649). A display region by the light emitting elements 103 is generally arranged on the front surfaces (surfaces opposing each other) of the housings 101, 201 in relation to attaching a cover (not shown) for reinforcement or a protective cover (not shown) for preventing breakage of a front surface cover 112 (shown in FIG. 11), to be described later, to the side surface and the back surface of the housings 101, 201 of the light projector 100 and the light receiver 200, where operation abnormality of the multi-optical axis photoelectric sensor, the state (light receiving level) of alignment between the light projector 100 and the light receiver 200, and the like are displayed by a lighted state and a non-lighted state of the light emitting element 103 in addition to the presence of power supply and the presence of object detection.
FIG. 11 shows an internal structure of the light projector 100. The basic configuration of the internal structure of the light receiver 200 is common with the light projector 100, and thus the illustration and the description thereof will not be given here.
A circuit substrate 104 having the plurality of light projecting elements 102 mounted in a line at the surface, and a plurality of holders 106 made of synthetic resin holding a light projecting lens 105 for collecting the light emitted by each of the light projecting elements 102 are arranged and housed in the housing 101 of the light projector 100.
Each of the holders 106 has both ends supported by opposing side wall portions of the housing 101, and has a holding hole 109 passed through at the middle for holding the light projecting lens 105 and the light projecting element 102 in a state facing each other. The housing 101 is configured by a case main body 101 having the front surface opened, and a transparent front surface cover 110 for blocking the opening at the front surface of the case main body 111.
The plurality of light emitting elements 103 are respectively mounted at the side positions of the line of light projecting elements 102 on the circuit substrate 104 so that the light emitting surface faces the front surface cover 110, and a columnar light guiding body 108 for guiding the light emitted from each of the light emitting elements 103 to the front surface cover 110 is held by each of the holders 106. Each of the light guiding bodies 108 has an incident end face 108a for entering the light inside facing the light emitting surface of the light emitting element 103, and an exit end face 108b for exiting the incident light to the outside facing the front surface cover 110. The light flux emitted from the light emitting element 103 enters into the light guiding body 108 from the incident end face 108a, straightly advances through the light guiding body 108, and exits from the exit end face 108b. 
The light emitted from each of the light projecting elements 102 is projected towards the light receiver 200 from a central portion of the width of the front surface cover 110, and the light emitted from each of the light emitting elements 103 is guided to the side position in the width direction with respect to the light projecting portion at the central portion of the width.